build: import erlang.mk

- uses erlang.mk with upstream patch #139 for common_test support
- removes script creation but this can be added into erlang.mk relatively easily
docs: update for new build process
build: reindent tests too
Merge pull request #25 from skunkwerks/feature/use-erlang.mk

build: use erlang.mk instead of rebar

- uses erlang.mk with upstream patch #139 for common_test support
- removes script creation but this can be added into erlang.mk relatively easily (see #24 )
- needs to be able to include the git sha in `.app.src` file either in `{vsn, ...}` or in `{id, ...}`
docs: make README.md steps work again
channel: add gproc dependency
channel: request & release a new channel
worker: use gproc registration & handle options
options: tests now use new default options and gproc
swirl: bring user app in line with peer_worker API change
convert: one less function needed
worker: transient restart for clean gen_server stop
reindent: appease the pedants